initial commit of new configuration access logic

1. Introduced new configuration manager class (singleton) based on apache commons composite configurations to load the config files during initialization
2. New configuration properties and their default values are maintained as enums.
3. qpid configuration classes were moved to "org.wso2.andes.configuration.qpid" from "org.wso2.andes.server.configuration"
4. MQTT configurations moved into andes config file
5. Added "commons-jxpath" since it is required by "commons-configuration" to handle xpath queries.
6. Added meaningful comments to describe properties and their usage.

NOTE : There is a significant namespace refactor here. the qpid configuration classes were moved from "org.wso2.andes.server" package to the "org.wso2.andes.configuration.qpid" package. These sources are not modified by wso2, rather re-used.  

Further Refactoring : 
----------------------------------------------
This commit was not merged since it had conflicts. However, comments on this and further re factoring has been carried out in following pull requests : 

https://github.com/wso2-dev/andes/pull/170 , https://github.com/wso2-dev/andes/pull/172 , https://github.com/wso2-dev/andes/pull/180 , https://github.com/wso2-dev/andes/pull/185
This enum is used when reading each configuration property. So the 3 properties passed in each property here are : 

xpath : the xpath expression to find the property from the xml file.
defaultValue : the fallback value for the property in case the value in file is invalid
dataType : the data type of the property as used in the code. 

So the default value here is only one attribute that defines a configuration property.